Gas analysis: Certainty saves lives

When lives depend on it, as in the case of gases used in the measurement of flammable gases in mining atmospheres, the traceability to known standards and uncertainty of the measurement must be known.

The accuracy and validity of measurements and calibrations will be determined, to a large extent, by the quality of the analytical test equipment. This includes equipment for subsidiary measurements, for example, environmental conditions. Calibration of equipment in the laboratory before being put into service can only be as good as the equipment and standards used for the calibration. Afrox’s laboratory has an established programme and procedure for the calibration of its equipment.

Traceability can be described as the programme for calibration of equipment, particularly for accredited testing and calibration laboratories. This programme must be designed and operated so as to make sure that calibrations and measurements made by the laboratory are traceable to the International System of Units (SI) (Systeme International d’Unites).

A traceable gas reference mixture is one whose concentration has been determined through a chain of direct comparisons linking them to relevant primary standards of SI units of measurement. For gas reference mixtures the ultimate link is to a standard unit of mass. Traceability is becoming increasingly important as companies adopt quality systems such as ISO 9000 or ISO 17025. For facilities attempting to achieve this accreditation, traceability of measurements must be established.

As the national gas standards are regularly compared with those of other countries, this network of traceable mixtures extends internationally, enabling measurement results to be accepted internationally.

Measurement uncertainty is a measure of spread about the result of a measurement within which we can reasonably expect the true result to lie. This margin of doubt requires quantification so that when a calibrated reference gas mixture is assigned a concentration value, a plus/minus uncertainty value can also be assigned.

In order to quantify the uncertainty, a consistent and systematic approach is required to assess all the factors, which are likely to affect a measurement.

Afrox can provide more information about uncertainties of results on request, by contacting the customer service centre on 0860 020202.